Large-scale production of antibodies for biopharmaceutical applications involves the use of cell cultures that are known to produce antibodies, and antigen-binding portions thereof, exhibiting varying levels of heterogeneity, which may lead to either decreased product efficacy and stability or just the opposite depending upon the nature of the heterogeneity. One source of antibody heterogeneity involves C-terminal lysine residues, such as those found on the heavy chains of antibody molecules. For example, C-terminal lysines can potentially be present on both the heavy chains of an antibody (Lys 2), on either one of the heavy chains (Lys 1), or neither of them (Lys 0). Since lysine can carry a positive charge, antibodies lacking the basic C-terminal lysine(s) differ in their charge state from ones that contain the lysine, so that the distribution of lysine variants (% Lys 0, % Lys 1, % Lys 2 of the total lysine sum) can be detected using ion-exchange chromatographic methods, for example, using a ProPac WCX-10 Weak Cation-Exchange column for high-resolution separation of protein isoforms (Dionex, CA), or other methods known in the art, and subsequently quantified.
C-terminal lysine heterogeneity is commonly observed in biopharmaceutical antibody and protein compositions. However, the development of compositions comprising antibodies, or antigen-binding portions thereof, with lower or higher levels of certain lysine variants is an important, need in the biopharmaceutical industry.